The present invention relates generally to a treatment fluid composition, and more particularly to a gravel packing fluid composition that includes hydroxypropyl starch phosphate.
Unconsolidated formations, particularly those containing loose sand and soft sandstone strata, present constant problems in well production due to migration of loose sand and degraded sandstone into the wellbore as the formation deteriorates under the pressure and flow of fluid through the wellbore. One method of controlling sand migration includes gravel packing.
Gravel packing is commonly used as a sand-control method to prevent production of formation sand or other fines from a poorly consolidated subterranean formation. In this context, “fines” are tiny particles, typically having a diameter of 43 microns or smaller, that have a tendency to flow through the formation with the production of hydrocarbon. The fines have a tendency to plug small pore spaces in the formation and block the flow of oil. As all the hydrocarbon is flowing from a relatively large region around the wellbore toward a relatively small area around the wellbore, the fines have a tendency to become densely packed and screen out or plug the area immediately around the wellbore. Moreover, the fines are highly abrasive and can be damaging to pumping and other oilfield equipment and operations.
Placing a relatively larger particulate near the wellbore helps filter out the sand or fine particles and prevents them from flowing into the well with the produced fluids. The primary objective is to stabilize the formation while causing minimal impairment to well productivity.
The particulate used for this purpose is referred to as “gravel.” In the oil and gas field, the term “gravel” refers to relatively large particles in the sand size classification, that is, particles ranging in diameter from about 0.1 mm up to about 2 mm. Generally, gravel is selected for having properties of physical integrity and chemical stability. An example of a commonly used gravel packing material is sand having an appropriate particulate size range. In one common type of gravel packing, a mechanical screen is placed in the wellbore and the surrounding annulus is packed with a particulate of a larger specific size designed to prevent the passage of formation sand or other fines.
Conventional gravel packing fluids use viscosifiers that allow or permit the gravel to fall or settle before it is placed in the correct location in the wellbore. For example, uncrosslinked hydroxyethylcellulose, hydroxypropylguar, xanthan gum, diutan, and like permit the gravel to fall or settle to the low side of the tubing in long, highly deviated wells particularly when used with fluids containing high amount of brine (e.g., more than 10%).
Thus, there is a continuing need for improved methods and compositions for gravel packing.